Pressure switch

Details Pressure switch Pressure switch

2000-05-09

2001-02-27

Friedhofer, Michael (Department: 2832)

Electricity: circuit makers and breakers

Solid contact

Membrane type

C200S181000, C200S0830SA, C200S0830SA, C073S727000

Reexamination Certificate

active

06194678

ABSTRACT:

BACKGROUND OF THE INVENTION
1) Technical Field of the Invention
This invention relates to a pressure switch with an airtight chamber partially defined by a diaphragm for electrically switching thereof in response to the stress applied to the diaphragm.
2) Description of Related Art
Some types of pressure switches have been so far proposed for a use of automobiles and industrial machines, in which a diaphragm of the pressure switch formed by partially thinning the semiconductor substrate is applied. Referring to
FIGS. 16 through 18
, the details of the conventional pressure switch disclosed in JPA06-267381, as an example, will be described hereinafter.
The conventional pressure switch
100
as shown in
FIG. 16
basically comprises a silicon substrate
110
made of p-type single crystal and a glass substrate
130
. The silicon substrate
110
includes, in its middle portion, a depression
111
formed on one surface (top surface), a recess
112
formed on the other surface (bottom surface) opposing to the depression
111
, and a diaphragm
113
defined by and between the depression
111
and a recess
112
(with a thickness of several ten micrometers). The silicon substrate
110
further comprises a pair of p-type diffusion layers
114
,
115
, which are formed on the top surface, and spaced apart (electrically isolated) from each other through the depression
111
. A pair of terminal electrode pads
116
,
117
made of aluminum is also deposited on the top surface of the silicon substrate
110
for electrically connecting the pressure switch to the peripheral devices. A first wire layer
118
made of material such as aluminum is deposited on and extends along the diffusion layer
114
(left side), a side-wall, and a bottom of the depression
111
.
On the other hand, the glass substrate
130
is joined on the top surface of the silicon substrate
110
so that an airtight chamber (reference pressure chamber) is defined between the depression
111
and the glass substrate
130
. A second wire layer
131
also made of material such as aluminum is formed on a part of a bottom surface of the glass substrate
130
opposing the diffusion layer
115
(right side). The first and second wire layers
118
,
131
are opposing each other within the airtight chamber
119
, and each includes a contacting tip
120
,
132
made of titanium, respectively. The diaphragm
113
, when stressed, is deformed close to the glass substrate
130
so that the contacting tips
120
,
132
contact each other so as to electrically connect the terminal electrode pads
116
,
117
through the p-type diffusion layer
114
,
115
and the wire layers
118
,
131
. Thus, the pressure switch can be switched in accordance with deformation (incurvature) of the diaphragm.
The silicon substrate
110
is designed to include a pair of offset paths
121
,
133
pre-formed on the p-type diffusion layers
114
,
115
for offsetting the thickness of the wire layers
118
,
131
thereby to smoothen the joint surface where the silicon substrate
110
and the glass substrate
130
are joined together. In general, in order to achieve the high reliable pressure switch, the silicon substrate
110
and the glass substrate
130
should be hermetically sealed to define the airtight chamber
119
, thereby maintaining its airtightness for a long time period.
SUMMARY OF THE INVENTION
Nevertheless, according to the above conventional pressure switch, the pre-formation of the offset path
122
,
133
requires a precise control of the manufacturing process for the wire layers
118
,
131
as well as the offset path
122
,
133
, so that both layers and paths have the same thickness. In fact, such control is too difficult to be achieved, and a high productivity can hardly expected especially in a mass production line.
Referring to the silicon substrate
110
as shown in
FIG. 17
, the diffusion layers
114
,
115
are formed apart from each other via a region
122
, in which the diffusion layer is not deposited. In general, a surface of the diffusion layer, when grown, is swelled by approximately one micrometer than the original surface so that a micro-step is formed between regions in which the diffusion layer is deposited and not. Therefore, the micro-step caused by the thickness of the diffusion layers
114
,
115
as well as the thickness of the wire layers
118
,
131
should be taken into consideration in order to smoothen the joint surface between the silicon substrate
110
and the glass substrate
130
. Indeed, the glass substrate
130
is gapped apart from the silicon substrate
110
at the region
122
in which the diffusion layer is not deposited so that the pressure switch
100
is as shown in FIG.
18
. This causes a problem deteriorating the airtightness of the airtight chamber
119
thereby to reduce the reliability of the pressure switch
100
.
In addition to that, the formation of the contacting tips
120
,
132
made of material such as titanium causes each a step-like boss at the overlapping portions of the contacting tips
120
,
132
on the wire layers
118
,
131
, as clearly shown in FIG.
18
. In general, the contacting tips
120
,
132
should have the contacting surface as wide as possible in order to improve the electrical switching characteristics of the pressure switch
100
, for instance, to reduce a resistance between the wire layers
118
,
131
, to minimize the chattering that is a noise vibration, and to optimize the deviation of pressure among pressure switches that is necessary for activating thereof. This would require that the step-like bosses of the contacting tips
120
,
132
have complementary configurations each other, which is almost impossible to control to produce.
Further, as described above, the first wire layer
118
(left side) is formed on and extending along the diffusion layer
114
(left side), a side-wall and a bottom of the depression
111
. The first wire layer
118
is bent at the portion between the top surface of the silicon substrate
110
and the side-wall of the depression
111
, and at the portion between the side-wall and the bottom of the depression
111
, thus the first wire layer
118
is easily broken at those bending portions.
Therefore, the present invention addresses the difficulties and problems as mentioned above. The first object of the present invention is to provide a pressure switch with an airtight chamber of which airtightness can be maintained for a long time period.
The further object of the present invention is to provide a pressure switch, which switches with less chattering at a higher response speed, and requires the minimized stress necessary for activating the pressure switches.
The pressure switch according to the first aspect of the present invention, comprises: a first substrate having a first opposing surface and a diaphragm capable of being readily deformed by a stress applied thereto; a second substrate having a second opposing surface overlapped with the first opposing surface of the first substrate to form an airtight chamber between the first and second substrate; a contact mechanism including, a first and second contact deposited within the airtight chamber and on the first opposing surface of the first substrate, a third contact deposited within the airtight chamber and on the second opposing surface of the second substrate, capable of being electrically connected with the first and second contact in response to the deformation of the diaphragm; and a sealing member continuously surrounding the airtight chamber, the sealing member disposed between the first and second opposing surface, thereby hermetically sealing the airtight chamber off the atmosphere.
The pressure switch according to the present invention, further comprises; a first and second conductive layer deposited on the first opposing surface of the first substrate, the first conductive layer being continuously surrounded by and spaced apart from the second conductive layer; and wherein the sealing member is the second conductive layer.
In the pressure switch according to the presen

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